容器网络如何处理与.Net和Docker的端口映射？

Question

When creating a new.Net 5 Web Api project you can find this in the generated launchSettings.json file

"applicationUrl": "https://localhost:5001;http://localhost:5000",

So when running the project you can call the Api endpoint via

GET https://localhost:5001/weatherforecast

When adding Docker support for the project you might create a Dockerfile like

FROM mcr.microsoft.com/dotnet/sdk:5.0 AS build
WORKDIR /app

COPY *.csproj ./
RUN dotnet restore

COPY . ./
RUN dotnet publish -c Release -o out

FROM mcr.microsoft.com/dotnet/aspnet
WORKDIR /app
EXPOSE 80
COPY --from=build /app/out .
ENTRYPOINT [ "dotnet", "Api.dll" ]

Most sample files expose port 80 in that file. When running the Api in a Docker container via

docker run -p 8080:80 my-image

I have to change the call to

GET http://localhost:8080/weatherforecast

So I call port 8080 which maps to port 80 internally but how does port 80 map to port 5000 to forward the request to the Api? It works "somehow". Would someone mind explaining this container networking?

Answer 1

As docs say launchSettings.json file is used only for local development:

The launchSettings.json file:

• Is only used on the local development machine.
• Is not deployed.
• contains profile settings.

As for docker image - it has environment variable ASPNETCORE_URLS set to http://+:80 so app listens to 80 port and there is no mapping happening between 80 and 5000